This invention relates to digital communication networks and more specifically to a network interface unit of the type supplied by First Pacific Networks, Inc. of Sunnyvale, Calif. for control of a digital voice telephone network. In particular, the invention relates to communication link management between calls within a controlled network which allocates calls by time division multiplexing of time slots and calls coupled to the network through the network interface unit through a trunk external to the network.
This invention represents an improvement over the voice telephone link described in U.S. patent application Ser. No. 07/345,490 filed Apr. 28, 1989, (published PCT Application PCT/US89/01806), now abandoned, the content of which is incorporated herein by reference.
In the past, a network head end card multiplexer (NHC MUX) has been provided between an external trunk and an internal network. The internal network has operated according to a proprietary protocol in which a wideband medium is used with two channels, an upstream or transmit channel and a downstream or receive channel. Each node within the network is connected to both the transmit channel and the receive channel. Communication is wideband and frame based, each frame containing a plurality of time slots to be reserved or allocated to packets containing data representing calls, whether audio, data or video. In the past, the head end has automatically reflected all information on the transmit channel to a corresponding timeslot of the receive channel. Moreover, each time slot (set) has been permanently paired with another time slot. This pairing enables full duplex communication during any two-way conversation on the internal network. At the beginning of each call, there is an acquisition period. The acquisition period is a time during which a time slot pair is claimed for a two-way full duplex conversation. In the past, a transmitting party (internal caller node) "occupying" a transmit time slot listens on the receive channel during the receive time slot.
However, as is typically the case, when the call of an external party that is outside the network (external caller) is passed through the MUX (a bridging call),the call data was multiplexed into the internal network as if it were an internal call. Since the bridging call occupies only a single channel, and since the receive time slot is not sent back to the external caller on the receive channel, one-half of the time slots among the paired time slots is unused in this situation. What is needed is a mechanism for better utilizing the available resources in an environment where a party connected internal to a network is communicating with a party external to the network.